Ecosystem Stability Determined by Two Simple Factors

Ecosystem stability has three phases, a bit like ice, water and steam. Find out how a new study explains how ecologists could predict these phases by gathering only two simple pieces of information.

I live in a part of Canada’s Province of Ontario called the Headwaters. Four of the major rivers that feed the Great Lakes begin their course in the highlands around here.

The Great Lakes contain 18% of the world’s freshwater. As a result, they provide more than 40 million people with their drinking water.

The watersheds in the Great Lakes Basin also include 43 habitats where ecosystem stability is at risk. Known as Areas of Concern (AOCs), they’re experiencing water quality problems, loss of fish and wildlife habitat and contaminated beaches.

Environmental Habitats are Complex Systems

Environmental habitats are complex systems. Thousands of species typically interact within a unique geological setting.

Understanding, predicting and adapting to complex systems is always a major challenge for scientists and engineers. That’s what led scientists at the Massachusetts Institute of Technology (MIT) to try to sort out and simplify what affects ecosystem stability, and enables species to coexist.

Ecosystems have something in common with the weather, the economy and the human mind. They’re complex systems with a lot of moving parts and things going on inside them.

Impossible to Do Lab Experiments on Complex Systems

That makes them hard to understand and even harder to predict. It’s also impossible to do controlled experiments on such complex systems in a laboratory.

Jeff Gore is a professor of physics at MIT. He’s become interested in finding ways to test how predictions from theoretical physics apply to biological ecosystems.

So, he started a lab that uses microbes like bacteria or yeast to make controlled studies of how species interact. From these studies, the lab has shown how both competition and cooperation affect species populations and why those populations sometimes collapse.

Ecosystem Stability Similar to Three States of Matter

Last week, the journal Science published a paper by a team of researchers led by Jilian Hu, an MIT graduate student, with Professor Gore as the senior author. In this experiment, the researchers tested a model that’s similar to the idea of the three states of matter.

Just as matter can be solid, liquid or gaseous, scientists can think of three phases of ecosystem stability. These three ecosystem phases are “stable full existence,” “stable partial existence” and “unstable.”

The researchers set up bacteria communities containing between two and 48 species. They could also control the strength of species interaction by changing how much food they gave each community.

“Experimental Communities Where You Can Turn the Knobs”

“In order to see phase transitions in the lab,” Professor Gore explained, “it really is necessary to have experimental communities where you can turn the knobs yourself and make quantitative measurements of what’s happening.”

The experiments confirmed the existence of the three ecosystem phases. What’s fascinating is that the studies show that scientists can predict ecosystem stability from two simple factors instead of countless individual interactions.

Those two determinants are the number of species in the ecosystem and the strength of their interactions. Interestingly, the type of interaction, for example whether it’s predatory, cooperative or competitive is irrelevant.

Complex Systems Share Property called “Emergence”

Ecosystems seem to share a property with other complex systems that scientists call “emergence.” It refers to how the parts of a complex system do things together that they can’t do individually.

It’s a bit like the old saying that someone “can’t see the forest for the trees.”Apparently, studying each individual species in an ecosystem is an inefficient way to understand how the overall habitat works together.

Ms. Hu described her team’s findings this way. “While we cannot access all biological mechanisms and parameters in a complex ecosystem, we demonstrate that its diversity and dynamics may be emergent phenomena that can be predicted from just a few aggregate properties of the ecological community: species pool size and statistics of interspecies interactions.”

“A Few Aggregate Properties of the Ecological Community”

Scientists have often been criticized for being “reductionists.” That is, when they studied systems in the past, they tended to reduce them to their components and then study each part on its own.

Increasingly, scientists apply the idea of emergence, studying overall systems in terms of the relationships between their elements. We’ve all heard that “the whole is greater than the sum of the parts,” and emergence applies that principle to scientific theories.

Emergence seems to be related to the as-yet-unexplained, self-organizing property of nature and the universe. A galaxy, or even a rock, is something beyond the chemical elements that comprise it. In the same way, our minds are something more than the neurons that make up our brains.

Water PHASEs Have Two Factors – Pressure and Temperature

Physicists can explain the phases of water, ice and steam based on only two factors– pressure and temperature. They don’t have to study the hydrogen and the oxygen in the water separately or observe what every molecule is doing.

Instead, they can create a “phase diagram” outlining the transitions. Now, ecologists may be able to do the same thing for ecosystem stability.

“What’s amazing and wonderful about a phase diagram is that it summarizes a great deal of information in a very simple form,” says Professor Gore. “We can trace out a boundary that predicts the loss of stability and the onset of fluctuations of a population.”

EcosysteM PHASES Based Number of Species and InteractION

In the future, researchers may be able to focus on just two vital signs to predict the future of a forest, desert or arctic habitat. All they’d need to determine would be the number of species in the ecosystem and how much they interact.

Professor Gore described the potential approach like this. “We can make predictions or statements about what the community is going to do, even in the absence of detailed knowledge of what’s going on. These predictions are based purely on the statistical distribution of the interactions within this complex community.”

The team is building on these experimental results by looking at how the species flow between isolated habitats affects ecosystem stability. They’re hoping this will help explain how species diversity stays stable in places like islands, for example.

We always have more to learn if we dare to know.
Learn more:
What drives ecosystems to insability?
Emergent phases of ecological diversity and dynamics mapped in microcosms
Biodiversity Always Wins
Animal Movement Disruptions Threaten Biodiversity
Wolves and Beavers are Vital to Ecosystems

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